Fainting (cont.)

Medical Author:
Medical Editor:

What causes fainting (syncope)?

Decreased blood flow to the brain can occur because 1) the heart fails to pump the blood; 2) the blood vessels don't have enough tone to maintain blood pressure to deliver the blood to the brain; 3) there is not enough blood or fluid within the blood vessels; or 4) a combination of reasons one, two, or three above.

Heart rhythm changes

Heart rhythm changes are the most common causes of passing out, fainting, or syncope. While this may sound ominous, frequently the faint is due to a temporary change in normal body function.

Sometimes, the heart rhythm change is more dangerous and potentially life-threatening. The heart is an electrical pump, and if an electrical system problem exists, the heart may on occasion be unable to adequately pump blood, causing short term drops in blood pressure. The electrical issues may cause the heart to beat too quickly, too slowly, or erratically.

A rapid heart rate or tachycardia (tachy = fast + cardia = heart) is an abnormal rhythm generated in either the upper or lower chambers of the heart and may be life-threatening. Should the heart beat too quickly, there may not be enough time for it to fill with blood in between each heart beat, which then decreases the amount of blood the heart can deliver to the body. Tachycardias can occur at any age and may not be related to atherosclerotic heart disease.

With bradycardia, or a slow heart rate (brady = slow + cardia = heart), the heart's ability to pump blood may be compromised. As the heart ages, the electrical system can become fragile and heart blocks, or disruptions of the electrical system, can occur, causing the heart rate to slow down.

Aside from structural electrical problems with the heart, medications may be the culprit. When taking prescribed medications for blood pressure control [for example, beta blockers such as metoprolol (Lopressor, Toprol XL), propranolol (Inderal, Inderal LA), atenolol (Tenormin), or calcium channel blockers such as diltiazem (Cardizem, Dilacor, Tiazac), verapamil (Calan, Verelan and others), amlodipine (Norvasc)], the heart can on occasion become more sensitive to the effects of these drugs and beat abnormally slow and decrease blood output from the heart.

Medically Reviewed by a Doctor on 12/2/2013

Patient Comments

Viewers share their comments

Fainting - Describe Your Experience Question: Please describe your experience with fainting.
Fainting (Syncope) - Treatments Question: What treatment has been effective for your fainting?
Fainting (Syncope) - Causes Question: What caused your fainting (syncope)?
Fainting (Syncope) - Symptoms Question: What symptoms did you experience with your fainting (syncope)?
Fainting (Syncope) - Diagnosis Question: After fainting, what medical tests and exams did you have? What was the diagnosis?